The present invention relates to storage systems, and more specifically to managing data replication between storage systems.
It is common to require both read and write access to a synchronously replicated disk through more than one storage system at multiple locations. The typical solution is to use a single location (e.g., a storage system) to resolve ordering between the writes submitted from the various locations, and then process the writes on each replica. Until the write has been completed on each replica, the initial write submitted to the storage systems may not be completed. This means that the externally-visible write latency is the sum of the time taken to transmit a message to the resolving location, transmit a message from the resolving location to each replica furthest from it, process and complete the write at each replica, and transmit messages from each replica back to the originating location. The transmission between locations may take multiple milliseconds and the storage time may be multiple milliseconds. Thus, the time to process and complete a write may take tens of milliseconds.